The present invention relates to an electroacoustic conversion film used for an acoustic device such as a speaker, and to an electroacoustic converter, a flexible display, and a projector screen using the electroacoustic conversion film.
In a flexible display using a flexible substrate (for example, plastics) such as an organic EL display, it has been considered that a flexible piezoelectric film having a sheet shape is adopted as a speaker that can be integrated with a flexible display without impairing the lightweightness or flexibility.
For example, JP 2008-294493 A discloses a piezoelectric film in which an electrode layer is formed on each of both surfaces of a piezoelectric body layer made of a uniaxially stretched polyvinylidene fluoride (PVDF) film on which polarization processing has been performed at a high voltage.
Further, JP 2003-244791 A discloses that a composite piezoelectric sheet, which is obtained by molding a polymer sheet such as PVDF or an epoxy resin in which a large number of piezoelectric elements (piezoelectric ceramics) are mixed, is used as a piezoelectric film.
In a configuration in which such a piezoelectric film is used as a vibration plate, since the vibration plate having a single plane is used, there is a problem in that it is difficult to output a broad band, such as, for example, the entire audible range (20 Hz to 20 kHz), at a uniform sound pressure level.
Therefore, JP 2003-244791 A describes that it is possible to broaden a band by dividing a vibration plate composed of the piezoelectric film and a pair of electrodes into a plurality of regions and forming a curved portion in which the respective regions have curvatures different from each other.